1. Field of the Invention
This invention relates to a permanent magnet consisting of major ingredients of iron, platinum and niobium, with less than 0.5 atomic (Atm) % of impurities, which permanent magnet has an ultra-high coercive force and a very large maximum energy product.
2. Description of the Prior Art
As to conventional permanent magnets which use the order-disorder lattice phase transformation, Co-Pt alloys of even content in terms of number of atoms are known. With the Co-Pt alloys, an ultra-high coercive force and a very large maximum energy product can be obtained in the initial stage of transformation from a disordered .alpha. phase lattice into an ordered .gamma..sub.1 phase lattice, which transformation can be caused either by cooling of the alloy of .alpha. phase at a high temperature of about 1,000.degree. C. with a constant cooling speed followed by reheating at about 600.degree. C., or by water quenching followed by reheating.
The conventional Co-Pt alloy demonstrates better magnetic properties as compared with other alloys, but it has a shortcoming in that, since its ferromagnetic atom is cobalt whose magnetic moment is smaller than that of iron, there are limits in its magnetic properties; namely, its residual magnetic flux density is limited to 7.2 kG (kilo.multidot.Gauss) and its maximum energy product is limited to 12 MGOe (Mega.multidot.Gauss.multidot.Oersted).
To overcome the above small magnetic moment, one may think of replacing cobalt in the alloy composition with iron having a large magnetic moment. However, with conventional Fe--50Pt (50 Atm % of Pt) alloys, the transformation temperature from ordered the lattice of .gamma..sub.1 phase to the disordered .gamma. phase is very high, being about 1,320.degree. C., and even a quick cooling, such as water quenching, results in a fairly well ordered lattice in an over-aged state. Thus, good magnetic properties cannot be produced by mere replacing of cobalt with iron.